1. Field of the Invention
This invention relates to a magnetic tunneling junction device displaying a so-called magnetic tunneling effect having a three-layer structure of a magnetic metal layer/insulating layer/magnetic metal layer, in which the conductance of the tunneling current flowing if the insulating layer has a thickness of tens of Angstroms is changed in dependence upon the relative angle of the directions of magnetization of both magnetic metal layers.
2. Description of the Related Art
Reports have been made of the magnetic tunneling effect in which, in a three-layer structure of the magnetic metal layer/insulating layer/magnetic metal layer, the conductance of the tunneling current flowing in case the insulating layer has a thickness of tens of Angstroms depends on the relative angle of magnetization of both magnetic metal layers.
In this phenomenon, the magnetoresistance ratio can be theoretically calculated based on the polarizability of magnetization of both magnetic metal layers. For example, if Fe is used for both magnetic metal layers, an extremely large magnetoresistance ratio is predicted to be produced.
This prediction has not been realized for long. Recently, by the combination of Fe/Al2O3/Fe, an extremely large magnetoresistance ratio of approximately 18% at room temperature has been realized. Thus, not only the physical manifesting mechanism but also the application as a new electro-magnetic transducer element, for example, is attracting general attention.
With regard to the magnetic tunneling junction device, exploiting the magnetic tunneling effect, only basic research has been started in connection with formation of an insulating layer by sputtering oxidation or preparation of fine junction by photolithography.
The most crucial problem raised in this research is the frequent failure in producing changes in resistance due to defects in the junction portion. If pinholes or similar defects are present in the insulating layer for the magnetic tunneling effect, or if some portions of the junction element are structurally susceptible to destruction of insulation, electrical leakage occurs leading instantly to failure in production of changes in resistance.
It is therefore an object of the present invention to provide a magnetic tunneling junction device capable of stably manifesting the magnetic tunneling effect.
The present invention provides a magnetic tunneling junction device in which a first magnetic metal layer and a second magnetic metal layer are connected together by ferromagnetic tunnel junction via an insulating layer and in which the conductance of the tunnel current is changed by the relative angle of magnetization of these magnetic metal layers, wherein the ferromagnetic tunnel junction has a junction area of not larger than 1 10xe2x88x929 m2.
By reducing the junction area to an extremely small value, a probability of the pinhole existing in the junction portion is reduced to exhibit the magnetic tunneling effect stably.
According to the present invention, the junction area of the ferromagnetic tunnel junction needs to be controlled positively. To this end, the insulating layer, for example, is preferably formed by the first insulating layer for ferromagnetic tunnel junction and a second insulating layer formed on the first insulating layer for limiting the junction area for the ferromagnetic tunnel junction.
This reliably limits the junction area of the ferromagnetic tunnel junction and provides a structure having excellent insulating properties for displaying the magnetic tunneling effect in higher stability.
According to the present invention, the magnetic tunneling effect can be displayed stably by prescribing the junction area of the ferromagnetic tunnel junction to a pre-set value.